If S and H are strength and hardness index of a timber at 12% moisture content, the composite sleeper index, is

• A. <img src="/_files/images/civil-engineering/railways/53-17-61-1.png">
• B. <img src="/_files/images/civil-engineering/railways/53-17-61-2.png">
• C. <img src="/_files/images/civil-engineering/railways/53-17-61-3.png">
• D. <img src="/_files/images/civil-engineering/railways/53-17-61-4.png">